Initiator



R. J. MILLER Oct. 15, 1963 INITIATOR Filed Dec. 27, 1961 States ate t 3,l@,892 Patented Get. 15, 1963 Free 3,166,892 INITIATOR Ross Jay Miller, Pitman, Ni, assignor to E. I. du Pont de Nemours and Company, Wiimington, Del, a corporation of Delaware Filed Dec. 27, 1961, Ser. No. 162,412 3 Claims. (Cl. 10227) The present invention relates to a non-electric initiating device.

US. Patent 2,982,210 discloses a connecting cord which comprises a continuous core of a detonating explosive, at 'a loading from 0.5 to 2 grains per foot of length, contained within a metal sheath and one or more layers of reinforcing and/or waterproofing material. Because it propagates a detonation impulse without brisance and is free from the hazards associated with electric initiators, in many blasting operations this cord has replaced conventional detonating fuse and electric initiators. However, the cord does not initiate all of the explosive compositions conventionally used in blasting. Consequently, auxiliary means are needed. In cases where it is desirable to provide a delay interval between initiation of the main explosive charges, a delay initiator actuated by the detonation of the connecting cord must be used. 'For reliable functioning in the field, the initiator must be ventless and capable of withstanding heavy water hammer effects even in water under considerable pressure.

In accordance with this invention an initiator is provided which comprises a tubular shell integrally closed at one end, said shell housing, in sequence from the closed end, a base charge of a detonating explosive, a primary charge of a heat-sensitive detonating explosive, a charge of an exothermic-burning composition, a tubular spacing member, one extremity of said spacing member being positioned contiguous to said exothermic burning composition, the other extremity of said spacing member forming an anvil head, a percussion-sensitive ignition composition contiguous to said anvil head, a cylindrical capsule open at one end housing said spacing member and said percussion-sensitive charge, said capsule being positioned with said open end abutting said exothermic composition, and said closed end being contiguous to said percussion-sensitive ignition charge, a booster charge of a detonating composition positioned in said shell in abutting relationship to the closed end of said capsule, and a low-energy connecting cord extending into said shell with the end thereof adjacent to and facing said booster charge.

In a preferred embodiment of this invention, the booster charge is encased in a cylindrical carrier, preferably of a ductile material, which fits snugly within the shell. The booster charge is of a composition essentially the same as that in the connecting cord but at a greater explosive loading, but of insufficient loading to initiate commercial dynamites in which the detonator may be embedded. In another preferred embodiment of this invention, a delay carrier is positioned between the exothermic-burning charge and the heat-sensitive detonating explosive charge.

The capsule housing the percussion-sensitive charge and the tubular spacing means is positioned in snug peripheral engagement with the inner wall of the tubular shell to insure that water or moisture will not seep past it to the exothermic burning composition.

In order to describe the invention in greater detail, reference is made to the accompanying drawings wherein:

FIGURE 1 is a cross-sectional view of an initiating assembly in accordance with this invention, and

FIGURE 2 is a cross-sectional view of an initiating assembly adapted to give a more delayed initiating ction.

In FIGURE 1, 1 represents a tubular shell having one integrally closed end, 2 represents the connecting cord consisting of the core 3 of a detonating explosive, metal sheath 4, and countering 5. The cord closes the open extremity of the shell and is held in place within the shell by peripheral crimps 6. Within shell 1 are, in sequence from the integrally closed end, a base charge 7 of a detonating explosive, a priming charge 3 of a heat-sensitive detonating explosive, an exothermic burning composition 9 and tubular spacing means 10, the upper surface of the walls of the tubular spacing means forming an anvil head 18 and the space within the tubular spacing means providing an air-gap 19. A charge of a percussion-sensitive charge 12 is contiguous to this spacing means. The open end of cylindrical capsule 11 fits over the tubular spacing means thus encasing the percussion charge. A booster charge 13 of a detonating charge, here shown in carrier 14, abuts capsule end 16 between booster charge 13 and percussion-sensitive charge 12.

The assembly depicted in FIGURE 2 is identical to that of FIGURE 1 except that a delay composition 17 encased in a delay carrier 15 is interposed between the priming and exothermic burning compositions.

In operation of the initiator, the initiation impulse propagated by the detonation of the explosive 3 within the core of connecting cord 2 is transmitted to the booster charge 13. The booster charge detonates thereby boosting or intensifying the detonation impulse transmitted to the capsule end. The detonation front progressing through the booster charge meets the capsule end 16, which is given a mechanical blow or knock sufiicien-t to push the percussion-sensitive charge against the anvil provided by the spacing member analogous to the action of a firing pin acting upon an impact-sensitive composition. Hot particles produced upon actuation of this charge jump the air gap 1.9 provided by the spacing element and ignite the exothermic burning composition 9. This composition burns at a high temperature, and when the hot front reaches the priming charge 8, the latter is ignited. The priming charge in turn initiates base charge 7. The initiator of the design of FIGURE 1 can be designed to provide a precise delay of from 1 to milliseconds, the length of the delay period depending upon the depth of the exothermic burning composition, since the burning time of the exothermic burning charge is proportional to the depth of this charge. A longer delay, e.g., 100 milliseconds to 20 seconds, is provided by the assembly of FIGURE 2 wherein the exothermic burning of delay composition 17 ignites the priming charge 8.

The water resistance of the present initiator is insured by the arrangement of the capsule and the spacing member within the tube such that seepage of water into the shell will not retard the transmission of mechanical force to the percussion-sensitive charge and dcsensitizing amounts of water cannot reach the priming and detonating charges. It is, however, essential for waterproofness that the closed end of the tubular capsule be capable of appreciable deformation without rupture by the blow given upon the impingement of the detonation front yet not of such great strength that force applied by the booster charge will not deform it even if the booster charge and capsule end are separated somewhat. Rupture or fracture of the end would cause venting and allow desensitizing amounts of water to contact the explosive charges. The capsule and particularly the diaphragm formed at the closed end of the capsule may be formed of any material which is ductile, malleable, and imperforate at the internal pressures developed by the charges inside the capsule. Exemplary materials include copper and copper alloys such as commercial bronze and brass, aluminum, steels, lead, nickel and the like or polymeric materials possessing similar physical characteristics. The thickness of the end naturally will be determined from the physical characteristics of the material used and the explosive loading of the initiator.

We have found that with booster explosive loadings of 2 to grains using aluminum or a copper alloy the capsule end will have a thickness of 0.010 to 0.030 inch. At thicknesses less than 0.010 inch, the end will be too fragile during loading of the shell Whereas at thicknesses greater than 0.030 inch the end will be too resistant to deformation.

The percussion-sensitive charge must be sensitive to impact or friction, rather than to flame or heat as are charges used hitherto in blasting initiators. Exemplary of charges suitable for use include lead styphnate, boronred lead mixtures, magnesium-, barium peroxide-, and selenium mixtures, bismuth-, seleniumand potassium chlorate mixtures, lead styphnate-, tetracene-ground glass mixtures and the like. Since ignition of the charge is by impact, the charge should be kept as small and as thin as possible to prevent cushioning. In general, the depth of the percussion-sensitive charge in the capsule will be the order of 0.010 to about 0.030 inch.

The presence of the booster charge of a detonating explosive is critical for reliable functioning of the initiator. Due to the extremely low loading of the low-energy connecting cord and the difliculty in obtaining a smooth, clean cut end of cord even with the most efiicient cutting means, the detonation front transmitted from the end of the cord is insufiicient to impart the requisite mechanical blow unless the cord is in a perfect contiguous relationship with the capsule end. The detonation of the booster charge, which is sensitive to the low energy detonation from this cord, intensifies the detonation impulses such that the detonation front impinging the capsule end is sufficient to insure reliable initiation of the percussionsensitive charge. The presence of the booster charge eliminates any requirement that the cord be perfectly cut, inserted and positioned since the booster charge is initiated even when separated from the end of the cord by an air gap of up to inch. The booster charge preferably Will be a detonating explosive of essentially the same explosive characteristics as the explosive composition comprising the core of the low-energy detonating cord and is at a greater explosive loading, e.g. 2 to 5 grains per foot. For ease of assembly and for nonviolent action, the booster charge preferably is enclosed in a carrier, eg. of lead or a similar ductile material.

The air gap or distance between the percussion charge and the dela composition is regulated, for example to focus the initiation impulse, by the provision of a spacing means. This spacing means preferably is a tube or capsule whose depth may be varied and whose side wall thickness or surface area contiguous the percussion-sensisive charge provide an unyielding anvil, i.e., ledge, against which the percussionasensitive charge is propelled. In general, the tube should not exceed /2 inch in length, a separation of greater than /2 inch results in unreliable functioning of the device.

In order to illustrate specific embodiments of the initiator of this invention in greater detail, reference now is made to the following examples. These examples are to be understood to be illustrative only and not limiting the invention in any way.

Example 1 Ten initiators were prepared resembling that of FIG- URE 1. In each case, the aluminum shell, 2.0 inches in length, 0.240 inch-outer diameter, had an 0.210 inch inner diameter. As a base charge, 5.0 grains of PETN was charged into the shell and pressed with a pointed pin at 200 pounds. Above this charge, 2.0 grains of lead azide, as a primer, was loaded and pressed at 200 pounds by a flat pin. The exothermic burning delay composition, 5.0 grains of a 2/ 98 boron/red lead mixture, was charged to each shell and pressed with a flat pin at 100 pounds. One grain of a 2/ 98 boron/red lead composition was pressed into a 0.562 inch long capsule open at one end (0.220 inch inner diameter, 0.190 inch outer diameter, bottom thickness, 0.018 inch); and the open end of the capsule was placed over a 0.750-inch long empty tube having a 0.067- inch central apenture and crimped in place. The free end of the tube was inserted into the shell and butted against the delay load mixture. A 0.25-inch long, 0.217 inch outer diameter booster carrier containing 0.114 grains of PETN Was pressed into the shell at 100 pounds pressure; The end of a length of low-energy connecting cord having an explosive loading of 2 grains of PETN per foot of length was inserted into the assembled initiator until the inserted end was adjacent to the booster carrier, and the shell crimped about the cord and the portion of the shell adjacent the capsules. When fired, the initiator gave a delay time of 56.7 milliseconds.

Example 2 A long-period delay initiator was assembled in an aluminum shell having essentially the same dimension as the shell discussed in Example 1 except that a longer shell was required to accommodate the charges. PETN and lead azide, as the base and priming charge, respectively, were loaded and compacted as in Example 1. A delay carrier having a length of 0.500 inch and a shell-wall thickness of 0.063 inch and containing a l.5/23.5/75.0 boron/red lead/dibasic lead phosphite, as a slow burning delay composition was placed adjacent the primer. One grain of a 2/98 boron/red lead mixture grained with Thiokol was loaded into the base of an 0.02.2-inch-long bronze tubular capsule having one open end, bottom thickness, 0.018 inch; and the end of the capsule was placed over an open-ended empty aluminum capsule, 0.469 inch long, and crimpcd in place. The thusassembled capsules were inserted into the shell, with the open end of the inner capsule facing the delay carrier and butted against the delay carrier. A-n 0.500 inch long, 0.217 inch outer diameter, 0.190 inch inner diameter booster. carrier containing a central core of lead azide was pressed into the shell at 200 pounds pressure. The end of a length of low-energy connecting cord having an explosive loading of one grain per foot of length was inserted into the shell until the inserted end was adjacent the booster charge and the shell was crimped about the cord. Upon being fired, the initiator gave a delay period of 1.09 seconds.

Similar results were obtained when lead styphnate, 2/ 98 boron/red lead, 30/35/35 magnesium/barium peroxide/selenium, and 62/ 35/ 3 bismuth/selenium/potassium chlorate were used as the percussion-sensitive charges.

The particular compositions used for the various base and priming charges are not critical to the instant invention, provided that the selected compositions function as desired. Accordingly, for the base charge, any of the usual base charges may be used, e.g., pentaerythritol tetranitrate (PETN) cyclotrimethylenetrinitratmine (RDX), lead azide, nitromannite, cyclotetramethylenetetranitramine (HMX) and the like. As the priming charge, heat sensitive detonating compositions such as lead azide, diazodinitrophenol, or mercury fulminate may be used. Obviously when squib action if desired, the priming composition and the base charge may be identical. The base and priming charges may be compacted by various shaped pins, e.g., conical, flat, pointed, or hell. Any compaction pressure sufiicient to retain the charges in the shell without causing their desensitization is suitable.

For the exothermic burning composition, an exothermically reacting mixture of a metal and an oxidizing agent of the type conventionally used in ventless delay initiators is preferred, e.g., boron-red lead, boron-red lead-dib-asic lead phosphite, magnesium-barium peroxide-selenium, or silicon-red lead. For longer period delay initiators, the :delay composition within the relay carrier may be any of the conventional gasless delay compositions which bum at a constant rate, such as a mixture comprising barium peroxide and selenium, bismuth, selenium, and potassium chlorate, lead and selenium, or magnesium and barium eroXide. The amount of each charge is varied depending upon the effect desired. The delay period is dependent upon the depth of the delay charge and the degree of compaction of the exothermic burning composition. The limits of pressure used to compact this charge are identical to those used for the base and priming charge, i.e., sufiicient to retain the composition in the shell without desensitizing the charge. If desired, the composition may be grained prior to use for example, with neoprene, gum, shellac, polyethylene glycol, Thio- K01, and carbowaxes, to facilitate loading. Obviously many modifications and variations are possible in View of the above teachings. Accordingly, within the scope of the appended claims the invention may be practiced otherwise than specifically described.

What is claimed is: 1. A non-electric delay initiator for actuating explosive blasting compositions consisting essentially of:

(a) a tubular shell integrally closed at one end, said shell housing, in sequence from said closed end, (b) a base charge of a detonating explosive composition, (0) a priming charge of a heat-sensitive detonating composition, (d) a charge of an exothermic burning composition, (e) a tubular spacing member, one extremity of said spacing member being positioned contiguous to said 6 exothermic burning composition, and the other extremity forming an anvil head,

(7) a percussion-sensitive ignition composition contiguous to the anvil head,

(g) a cylindrical capsule open at one end, said capsule housing said spacing member and said percussionsensitive composition and said capsule being positioned in said shell with said open end abutting said exothermic composition and said closed end contiguous to said percussion-sensitive ignition charge,

(11) a booster charge of a detonating composition abutting the closed end of said capsule, and

(i) low-energy connecting cord extending into the shell with the end thereof adjacent to and facing said booster charge.

2. An initiator as in claim 1 wherein said booster charge is encased in a cylindrical metal carrier which fits snugly within the shell and is of essentially the same composition as that in the connecting cord.

3. A initiator as in claim 1 wherein a delay carrier comprising a heavy walled-tube of a rigid material containing a central core of delay composition is interposed between said priming charge and said exothermic-burning composition.

References Cited in the file of this patent UNITED STATES PATENTS 2,478,415 Miller Aug. 9, 1949 2,736,263 Lewis et a1. Feb. 28, 1956 2,857,845 Seavey Oct. 28, 1958 2,982,210 Andrew et a1. May 2, 1961 FOREIGN PATENTS 627,435 Canada Sept. 12, 1961 

1. A NON-ELECTRIC DELAY INITIATOR FOR ACTUATING EXPLOSIVE BLASTING COMPOSITIONS CONSISTING ESSENTIALLY OF: (A) A TUBULAR SHELL INTEGRALLY CLOSED AT ONE END, SAID SHELL HOUSING, IN SEQUENCE FROM SAID CLOSED END, (B) A BASE CHARGE OF A DETONATING EXPLOSIVE COMPOSITION, (C) A PRIMING CHARGE OF A HEAT-SENSITIVE DETONATING COMPOSITION, (D) A CHARGE OF AND EXOTHERMIC BURNING COMPOSITION, (E) A TUBULAR SPACING MEMBER ONE EXTREMITY OF SAID SPACING MEMBER BEING POSITIONED CONTIGIOUS TO SAID EXOTHERMIC BURNING COMPOSITION, AND THE OTHER EXTREMITY FORMING AN ANVIL HEAD, (F) A PRECUSSION-SENSITIVE IGNITION COMPOSITION CONTIGUOUS TO THE ANVIL HEAD, (G) A CYLINDERICAL CAPSULE OPEN AT ONE END, SAID CAPSULE HOUSING SAID SPACING MEMBER AND SAID PRECUSSIONSENSITIVE COMPOSITION AND SAID CAPSULE BEING POSITIONED IN SAID SHELL WITH SAID OPEN END ABUTTING SAID EXOTHERMIC COMPOSITION AND SAID CLOSED END CONTIGUOUS TO SAID PRECUSSION-SENSITIVE IGNITION CHARGE, (H) A BOOSTER CHARGE OF A DETONATING COMPOSITION ABUTTING THE CLOSED END OF SAID CAPSULE, AND (I) LOW-ENERGY CONNECTING CORD EXTENDING INTO THE SHELL WITH THE END THEREOF ADJACENT TO AND FACING SAID BOOSTER CHARGE. 